1. Field of the Invention
The present invention relates to an anisotropically conductive sheet suitable for use, for example, in electrical connection between circuit devices such as electronic parts, or as a connector in inspection apparatus for circuit devices such as printed circuit boards and semiconductor integrated circuits, a production process thereof, and a connector.
2. Description of the Background Art
An anisotropically conductive elastomer sheet has a conductor exhibiting conductivity only in its thickness-wise direction or a pressure-conductive conductor exhibiting conductivity only in its thickness-wise direction when it is pressurized in the thickness-wise direction. Since the anisotropically conductive elastomer sheet has features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection between a circuit device, for example, a printed circuit board, and a leadless chip carrier, liquid crystal display panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
The anisotropically conductive elastomer sheet is also used as a sensor for detecting external force in a key board, touch switch or the like.
Further, in electrical inspection for electronic circuits or semiconductor integrated circuits fabricated by various materials in accordance with various methods, such as printed circuit boards, flexible boards, ceramic boards or a carrier tape for TAB, or MCM in which a plurality of semiconductor integrated circuits are incorporated into a module, it is conducted to interpose an anisotropically conductive elastomer sheet between an electrode region to be inspected and an electrode region for inspection in order to achieve electrical connection between electrodes to be inspected formed on at least one surface of a circuit device which is a inspection subject and electrodes for inspection formed on the surface of a circuit board for inspection.
As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses anisotropically conductive elastomer sheets obtained by uniformly dispersing metal particles in an elastomer, Japanese Patent Application Laid-Open No. 147772/1978 discloses anisotropically conductive elastomer sheets obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating parts for mutually insulating them, and Japanese Patent Application Laid-Open No. 250906/1986 discloses anisotropically conductive elastomer sheets with a difference in level defined between the surface of the conductive path-forming parts and the insulating parts.
However, since an anisotropically conductive sheet has conductivity in its thickness-wise direction and insulating property in its plane direction, static electricity is generated on the surface of the anisotropically conductive sheet according to manner of usage or service environment to offer various problems due to charging.
For example, when an anisotropically conductive sheet is used in electrical inspection for circuit devices, the anisotropically conductive sheet is interposed between a circuit device (hereinafter may be referred to as “circuit device to be inspected”) which is an inspection subject to be inspected and a circuit board for inspection, the anisotropically conductive sheet is pressurized, thereby achieving electrical connection between the circuit device to be inspected and the circuit board for inspection to conduct electrical inspection. However, an electric charge is easy to generate by pressurizing operation and separation operation, so that when the electrical inspection of a great number of circuit devices to be inspected is continuously conducted, the electric charge is accumulated on the surface of the anisotropically conductive sheet which comes to bear high-voltage static electricity.
When the electric charge is accumulated on the surface of the anisotropically conductive sheet to bear the static electricity, the circuit device to be inspected is stuck on the anisotropically conductive sheet by such static electricity. It is thus difficult to smoothly conduct the inspecting operation. When high-voltage static electricity is accumulated on the anisotropically conductive sheet, inconvenience is encountered on the security of operator's safety. When extremely high-voltage static electricity is accumulated in particular, an adverse influence by discharge of the static electricity may be exerted on not only the inspection apparatus and the anisotropically conductive sheet, but also the circuit device to be inspected in some cases. As a result, there is a possibility that the circuit board for inspection and inspection apparatus may go wrong, or the circuit device to be inspected may be broken.
For such reasons, it is necessary to stop inspecting operation periodically or as needed at the time the generation of static electricity is observed on the surface of the anisotropically conductive sheet, so as to conduct static charge-eliminating operation by means of a static charge eliminating brush or the like. Therefore, there is a problem that inspection efficiency is lowered.